This invention relates to a high-pressure discharge lamp provided with a discharge tube with a current lead-through member through an end of the discharge tube, and provided with a heat shield around the end of the discharge tube. The invention also relates to a heat shield suitable for use in a high-pressure discharge lamp as described above.
A lamp of the kind mentioned in the opening paragraph is known under the designation Philips SON-T Comfort 400 W. The heat shield serves to influence the heat balance of the discharge tube (d.t.) so that a desired temperature prevails at the area of the d.t. end during nominal lamp operation. The temperature at the area of the d.t. end, called cold spot temperature T.sub.kp hereinafter, determines the pressure of filling ingredients present in excess quantity in the discharge tube during lamp operation.
The heat shield in the known lamp is constructed as an Nb strip which is fastened to an Nb bush of the current lead-through member by means of an Nb rod. The heat shield narrowly surrounds the end of the discharge tube. The Nb rod ensures that the Nb strip is fixed relative to the discharge tube end.
The known construction has the major disadvantage that the Nb rod must be welded both to the Nb strip and to the Nb bush for fastening the Nb strip. In practice, in the manufacture of large numbers of lamps, this leads to a considerable spread in the fixed positions of the heat shields, and thus to a spread in T.sub.kp. In addition, this fastening is a comparatively labour-intensive operation which does not lend itself readily to mechanization. Bush-shaped heat shields have been proposed in the literature, where the current lead-through member projects through the bottom of the bush-shaped shield and where the shield is fastened to the current lead-through member by means of a welded or soldered joint. Although a welded or soldered joint need be made in a single location only in this construction, the problem of spread in the positions remains unaffected.